1. Field of the Invention
The present invention relates to a multilayer printed wiring board in which electronic components, semiconductor device and the like are mounted on the front face of a board thereof and a manufacturing method thereof and more particularly a multilayer printed wiring board preferably used for portable telephone, portable electronic appliance, electronic package and the like and a manufacturing method thereof.
2. Description of the Related Art
A unit of the circuit board is formed by drilling via holes in an insulation hard base material having a conductive circuit on at least one face and then forming conductive layer in their openings with metallic paste or plating. A multilayer circuit board (multilayer printed wiring board) can be obtained by preparing two or more pieces of these circuit boards and bonding those boards successively or collectively such that they are overlaid into multi-layers. At this time, because a via hole or a land of the via hole of one circuit board is connected to a conductive circuit or a land of the other circuit board, these two circuit boards are electrically connected. In other region in which no electrical connection is performed, circuit boards are fitted to each other with an adhesive layer composed of thermoplastic resin or prepreg. As a conventional art relating to these, Japanese Patent Application Laid-Open No. 10-13028 can be mentioned.
A solder resist layer for protecting the conductive circuit is formed on the front face of the board or a general printed wiring board and solder pads are formed by opening part of the solder resist layer. By exposing the conductive circuit through that opening, a corrosion resistant layer such as nickel-gold is formed on its front layer. The corrosion-resistant layer is formed on all the solder pads and solder is formed on a conductive circuit covered with the corrosion-resistant layer and then an electronic component is mounted thereon.